1. Field of the Invention
The invention is related generally to the field of wound fiber reinforced plastic articles. More specifically, the invention is related to particular structures for such articles which have increased pressure carrying capacity.
2. Description of the Related Art
Wound fiber reinforced plastic tubing is known in the art, particularly for use as a substitute to steel tubing in certain applications. Typically, wound fiber reinforced plastic tubing includes an inner impermeable liner, which can be made from thermoplastic or the like, and has various types of fiber wound on the exterior of the liner in a selected pattern. The fiber can be glass, carbon, aramid or other type of fiber, or combinations of fiber types, depending on the mechanical requirements for the finished tubing. The fiber can be impregnated with resin prior to, during, or after winding. The resin is typically a thermoset resin, and can be cured by various types of heating systems.
A very useful type of wound fiber reinforced plastic tubing includes a combination, typically half by volume each of carbon fiber and glass fiber forming each layer of fiber wound on the liner. The carbon and glass fibers are wound in a substantially helical pattern, in a plurality of layers, over the exterior of the liner. The carbon and glass fiber are disposed in alternating spools on a winding machine during the wrapping process. The resulting layer of fibers wound on the liner is known as a “intralaminar hybrid” layer because it is made up of more than one type of fiber within the layer. The reason that the intralaminar type of layer has proven useful is that it provides the finished tubing with substantial flexibility related to the lower stiffness, more flexible glass fibers, while substantially improving the pressure carrying capacity of the finished tubing over that of tubing wound only using glass fiber to reinforce the liner. As is known in the art, flexibility in the finished tubing is important because the finished tubing is typically wound on large reels or spools for transport and use in the intended application for the tubing.
A limitation of the intralaminar hybrid composite tubing known in the art is susceptibility to failure at internal fluid pressures lower than would be expected given the composite mechanical properties of the fiber layers wound around the liner. The carbon fiber in the typical intralaminar hybrid layer tubing provides a calculable increase in the expected pressure carrying capacity of the finished tubing, but practical fiber reinforced tubing made using intraminar layers method have generally not provided a pressure carrying capacity commensurate with the increased strength of the carbon fiber.
It is desirable to have a wound fiber reinforced plastic tubing which has a pressure carrying capacity more closely related to that expected by providing composite fiber layers on the tubing.